With the transition from analog to digital TV broadcasting comes the availability of bandwidth for new generations of wireless devices. After the transition, many channels become available, especially the upper ranges of the TV bands such as channels 14-83, also known as ultrahigh frequency or UHF. These available channels are vacant frequencies. The FCC is considering freeing up this so-called “white space” spectrum to unlicensed devices (a.k.a. white space devices or WSD) in order to promote a more effective use of the public airwaves. The envisioned WSDs include but are not limited to high-speed wireless network connections and cable-less home entertainment systems. These WSDs present new opportunities for consumers to efficiently use currently unused spectrum. With the growing use of Wi-Fi and other unlicensed devices in everything from laptops to next-generation PDAs and cell phones, WSDs provide much-needed additional capacity for broadband connectivity and home and community networking.
WSDs are expected to operate in a cognitive manner by sensing and detecting over-the-air digital TV (DTV) signals and avoiding these occupied frequency bands. However, cable TV (CATV) also shares part of this “white space” spectrum. Hence WSDs avoiding over-the-air DTV band may still cause interference to television receivers connected to CATV service. Such interference was confirmed in tests and reported by the FCC in “Direct-pickup interference tests of three consumer digital cable television receivers available in 2005,” by S. R. Martin (OET Report FCC/OET 07-TR-1005, Jul. 31, 2007) and “Evaluation of the performance of prototype TV-band white space devices phase II,” by S. K. Jones et al. (OET Report FCC/OET 08-TR-1005, Oct. 15, 2008).
The Oct. 15, 2008 report discussed the capability of prototype TV-band WSDs to detect over-the-air DTV signals. The tested prototype devices described in this report were provided by Adaptrum, the Institute for Infocomm Research (I2R), Microsoft Corporation (Microsoft), Motorola Inc., and Philips Electronics North America Corp (Philips). According to this report, the detection threshold sensitivity of the devices varied from −106 dBm to −128 dBm for the over-the-air DTV signals. The sensing times are 0.1 second/channel for the Motorola device, 37-185 seconds/channel for the Adaptrum device, and 8-50 seconds/channel for the Philips device. The other device sensing times are not specified in the FCC report.
Among these tested prototype devices, none has reported the ability to identify CATV usage information. The current white space identification is performed based on spectrum sensing, which is not effective for CATV.
However, the interference from these devices to CATV have been tested and proved to be non-negligible. In addition, both reports indicate that the interference effect is significant even for low power devices.
From the reported signal detection performance for over-the-air DTV signals, it can be inferred that it is essentially impossible for the prototype devices to sense and avoid CATV active channel since the signal leakage from the CATV (if any) is significantly weaker than over-the-air DTV signals, while the number of CATV channels is large.
As a result, obtaining knowledge on the active channel usage of CATV is critical for the identification of usable TV-band white space which complies with the FCC's regulation of “zero interference tolerance.”
Accordingly, there is a need in the art for a white space identifier directed for use with active cable TV channels.